1. Field of the Invention
The present invention relates to a light emitting device that radiates light from a point light source as parallel light or converging light.
2. Description of the Related Art
A light-emitting diode “LED”, which has good points such as low power consumption and long operating life as against a conventional incandescent lamp, for example a halogen lamp, is widely used, because people become more ecology conscious. And people consider that using the LED is one policy for the energy-saving strategies. Particularly, it is highly required to use the LED as an alternate item of the incandescent lamp.
As against the halogen lamp, or “a line or a plane” filament emits light, the LED is a “point light source” because of its small light-emitting area. This results in that the light reflected with a concave reflecting surface becomes parallel light, with “parabola” concave reflecting surface, or converging light, with “ellipsoid” concave reflecting surface, using the LED in higher degree of accuracy than using the incandescent lamp. Because the light-emitting center of the point light source can be located easily at the focal point, or near the focal point, of the concave reflecting surface defined by a paraboloid of revolution or an ellipsoid of revolution.
But the light directly emitted from the reflector cannot be controlled merely by combining the LED and the reflector. “Directly” means that the light from the LED is emitted without any reflection on the concave reflecting surface. Especially, the light from the LED is the strongest on its light axis usually; the larger the angle between the light axis and the light is, the smaller the strength of the light becomes. In short, the LED is “a directional light source.” Consequently, most of the light from the LED is emitted “directly” from the reflector without any reflection, or without any control, when the LED is located at inner-bottom of the reflector so that the light axis of the LED coincides with the center axis of the reflector. The center axis of the reflector is a center axis of rotation for the paraboloid of revolution or the ellipsoid of revolution.
On the other hand, according to the light source described in the Patent Document 1, Japanese Laid-Open Patent Publication No. 2005-347224, the LED is located at inner-bottom of the reflector defined by the ellipsoid of revolution so that the light axis of the LED coincides with the center axis of the reflector. Furthermore, a lens, with which the light on and near the light axis converges on the light-converging point by refracting, is provided on the light axis within the reflector.
According to such a light source in the Patent Document 1, the light on and near the light axis converges on the light-converging point by refracting on the lens. And the light which makes a large angle with the light axis of the LED is reflected on the concave reflecting surface and becomes the converging light to the light-converging point of the reflector as well as the light on and near the light axis.